ONE of the most eminent of the colaborers of Pasteur in the investigation of the relations of microorganisms to disease-infection, and one whose labors have been most fully appreciated by intelligent men, is Dr. Robert Koch, of Berlin. He was born at Clausthal on the 11th of December, 1843, the son of a high officer in the department of mines. He attended the gymnasium in his native town, and afterward — from 1862 to 1866 — studied medicine at Göttingen. He became an assistant in the Allgemeine Krankenhaus, or General Hospital, at Hamburg; began the practice of medicine in 1866 at Langenhagen in Hanover; then settled at Racknitz, in Posen. From 1872 till 1880 he was physikus or district physician at Wallstein, in the district of Bomst. He engaged in studies of bacteriological diseases, including wound-infections, septicaemia, and anthrax, or splenic fever, with, great success; and was appointed in 1880 a member in ordinary of the Imperial Health Office. In 1885 he was appointed a professor, and the director of the Hygienic Institute in Berlin.

The first public report of Dr. Koch's to attract general attention was that in reference to the bacterium which had been found associated with anthrax, or splenic disease, and was made about 1878. His investigations went to show that the potency of this organism lay in the spores rather than in the developed bacterium. He found that, when no spores were visible in the dried diseased blood with which mice were inoculated, the power of conveying infection lasted only for a few weeks; while blood in which the spores had separated continued virulent for at least four years.

He next turned his attention to those infectious disorders which originate in the introduction of poisonous matter through wounds. Living organisms had already been observed in these diseases, but their connection with the development of the infection had not been determined. Dr. Koch's experiments with small animals showed that different forms of disease were produced by the injection of putrid blood, one of which was not accompanied by the development of bacteria, but seemed due to a special poison which he named septin or sepsin, while another form was evidently bacterial; and that the effects varied with different animals.

In 1882 Dr. Koch published the results of experiments which went to confirm the opinion already held by physicians who had observed the progress of the discovery of the fungoid origin of various infections, that tubercular disease was also caused by microphytic germs. He claimed not only that he had ascertained the bacterial origin of the disease, but to have detected the specific microbe, having found a characteristic and previously unknown bacillus in all tubercularly altered organs. He had observed it in pulmonary tuberculosis, cheesy bronchitis and pneumonia, tubercles of the brain, intestinal tubercles, scrofulous glands, and fungous inflammation of the joints; in all cases which he had examined of spontaneous consumption in animals — in cattle, hogs, poultry, monkeys, porpoises, and rabbits. In monkeys dead of consumption he had found the organisms in quanities pervading the lungs, spleen, liver, diaphragm, and lymphatic glands. He supposed that, escaping into the air from the expectorations of phthisical patients, they were inhaled into the lungs, where they developed. Whenever the tubercular process was in its early and active stage, they were present in great numbers. When the climax of the tubercular eruption was passed, they decreased and might totally disappear.

Dr. Koch's report of this investigation was published in one of the Berlin medical journals, in a memoir on "The Etiology of Tuberculosis," of which Dr. Klein, a distinguished pathologist, said that any one who carefully reviewed it would "come to the conclusion that Dr. Koch's results are to be accepted with unconditional faith, and I have no manner of doubt will be considered by all pathologists as of the very highest importance. To those who are familiar with Dr. Koch's previous work, especially that on the etiology of splenic fever, or anthrax, and his observations on pathogenic bacteria, this last work of his, on the etiology of tuberculosis, will be an additional and brilliant testimony to his ingenious and successful method of research." This testimony is the more significant because Dr. Klein afterward disputed Koch's identification of the "comma bacillus" with the cause of cholera. In the next year a report was published by Mr. Watson Cheyne of a visit which he had made as a commissioner of the British Association for the Advancement of Medicine by Research, to the laboratory of Dr. Koch, and also to that of M. Toussaint, who was engaged in a similar investigation. It represented that such results of Toussaint as disagreed with those obtained by Dr. Koch were not borne out. But the result of inoculation with cultivations obtained from Dr. Koch was in all cases rapid development of tuberculosis. The examination of a large quantity of tuberculous material showed the constant presence of tubercle bacilli, but of no other micro-organisms. The rapidity and certainty of action of this matter, when inoculated into animals, was in direct ratio to the number of bacilli introduced, and the most certain and rapid means of inducing tuberculosis seemed to be the inoculation of the tubercle bacillus cultivated on solid blood-serum. These facts led Mr. Cheyne to the conclusion that these bacilli are the virus of the acute tuberculosis caused in animals by inoculation.

When the cholera broke out in Egypt in 1883, the German Government appointed Dr. Koch chief of a commission to go to that country, and also to India, for the purpose of watching the course of the epidemic and investigating the nature and cause of the disease. The report of the work of this commission in Egypt, published in the early autumn of 1883, while it did not make known any certain results of the investigation, and dealt "in a very guarded manner" with the question of the discovery of a definite cholera bacillus, pointed out the line on which future studies were to be pursued. In experiments carried on in both living and dead subjects, while no distinct organism could be traced in the blood and the organs which are most frequently the seat of micro-parasites, bacteria having distinct characteristics were found in the intestines and their mucous linings, under circumstances that seemed to identify them with the disease from which the patients were suffering. They were present in the case of all patients suffering from cholera, and in the bodies of all who had died of it, whereas they were absent in the case of one patient who had had time to recover from cholera, but had died of some secondary complication; and they were not discoverable in the case of patients who, during the cholera epidemic, succumbed to other diseases. They were also the same with the bacillus which Dr. Koch had met the year before in the bodies of patients who had died of cholera in India. From these causes the commission felt justified in provisionally holding the belief that those bacilli were in some way related to cholera, but were not yet prepared to say whether they were the cause or the effect of the disease. In 1884 Dr. Koch visited Toulon, where cholera was raging, partly at the wish of the French Government, which desired to know more of his methods of investigating and suppressing the disease.

The investigations of the German commission were continued in India, and Dr. Koch's report on the subject was published in the "Klinische Wochenschrift," of Berlin, No. xxxiv, 1884. He had found, in the rice-water discharges of patients suffering from cholera, besides the micrococci and bacilli common to the evacuations of other patients, peculiar curved bacteria, which have become known as "comma-shaped" bacilli, such as he had not been able to discover in any cases of diarrhoea; and he had succeeded in isolating them by artificial culture. This he declared to be a specific micro-organism having marked characteristics distinguishing it from all other known organisms. These organisms grow rapidly in meat-infusion and blood-serum, and well in other fluids, especially milk, and in potatoes; and possess the power of active motion. They grow best at a temperature of between 30° and 40° C, and cease to grow at 16° C, but are not killed by freezing. They grow only in the presence of oxygen, and very fast; their vegetation rapidly reaches its highest point, then remains stationary for a time, after which it ceases as rapidly as it grew, and the bacilli die. When dried, they die within three hours; and they do not form spores. Micro-organisms possessing all of these and certain more delicate characteristics which are definitely described, are Koch's bacilli; organisms presenting only some of the characteristics, such as microscopical appearance, are something else.

The presence of these bacilli in cholera, which was represented as universal, was determined by microscopical examination in ten cases in Egypt, and by microscopical examination and cultivation in gelatinous meat-infusion in forty-two cases of post-mortem examination in India; and in numerous other cases of dejections in Egypt, India, and Toulon — giving a hundred cases occurring in various parts of the world, carefully examined, in which the organisms were found. It had been further found that this was the only form of micro-organism that was constantly present in the disease; that it was present in greatest numbers in acute and uncomplicated cases, and in the parts most affected; while it was never present in other diseases, in healthy persons, and had not been found outside of the body where no cholera was in the neighborhood. Then, having disposed of two hypothetical presumptions of contrary tenor, Dr. Koch declared that no other conclusion could be arrived at than that these bacilli are the cause of cholera.

Although no effects had then been obtained from experiments with comma bacillus upon animals, and direct experiments upon man could not be performed, various observations confirming the theory had been obtained which were almost as good as experiments on man. In the water of a tank whence the inhabitants of a village near Calcutta derived their supplies for drinking, cholera bacilli were found in considerable numbers when the cholera epidemic was at its height. At a later period, when there were only a few cases of illness, the comma bacilli were few in number, and found only at one part of the tank. This was the only instance in which these bacilli were found outside of the body. Finally, Dr. Koch maintained that the natural history of the disease corresponds with the various characteristics of the organism in question The bacilli grow rapidly, soon reach their highest point of development, then die, in correspondence with what occurs in the intestinal canal. Under ordinary circumstances the bacilli are destroyed in the healthy stomach, while persons suffering already from some disorder of the stomach are most liable to be attacked with cholera. Lastly, the disease dies out in places where the conditions for its continuance are unfavorable; as bacilli that have no spores will speedily disappear. In experiments subsequent to this report, Dr. Koch succeeded in producing cholera by inoculation in some of the smaller animals.

Dr. Koch's conclusions were contested and some of his evidences were disputed by a French commission appointed to inquire into the causes of cholera; by certain English pathologists, including Dr. Klein and Dr. Lewis, of Netley; and were not fully supported by an English commission in India; but, while they may not yet have been fully accepted, they have not been overthrown, nor do they seem to have lost ground. A bill was unanimously passed by the German Parliament, in 1884, awarding a sum of 135,000 marks to Dr. Koch and his companions in this research.

The principal published works of Dr. Koch are "Etiology of Splenic Fever," 1876; "Researches on Diseases of Wound-Infections," 1878; "Inoculation for Splenic Fever," 1882; "Contributions to the Etiology of Tuberculosis," 1882; and contributions to the transactions of the German Imperial Health Bureau.